Method and apparatus for producing biofuel in an oscillating flow production line under supercritical fluid conditions

ABSTRACT

The invention discloses a method for producing bio-fuel (BF) from a high-viscosity biomass using thermo-chemical conversion of the biomass in a production line (10) with pumping means (PM), heating means (HM) and cooling means (CM). The method has the steps of 1) operating the pumping means, the heating means and the cooling means so that the production line is under supercritical fluid conditions (SCF) to induce biomass conversion in a conversion zone (CZ) within the production line, and 2) operating the pumping means so that at least part of the production line is in an oscillatory flow (OF) mode. The invention is advantageous for providing an improved method for producing biofuel from a high-viscosity biomass. This is performed by an advantageous combination of two operating modes: supercritical fluid (SCF) conditions and oscillatory flow (OF).

FIELD OF THE INVENTION

The present invention relates to a method for operating an oscillatingflow production line in a production system, e.g. a hydrothermalreactor, to produce bio-fuel, or bio-based chemicals, from biomass, suchas lignin material from straw. The invention also relates to acorresponding production line or production system.

BACKGROUND OF THE INVENTION

15 Bio-fuel and bio-based chemicals production is an area of intenseresearch and development because of the world-wide transition fromfossil fuel to climate neutral fuels, such as biofuels produced frombiomass, e.g. as waste product from agricultural production. Methodsusing super-critical fluid conditions (SCF) for biofuel production bythermo-chemical conversion have been known for some time. Notice thatthermo-chemical conversion is sometimes referred to as hydrothermalconversion or hydrothermal liquefaction, the conversion mainly beingcontrolled by the availability of additional chemicals and catalysts,and conversion temperature as well as pressure. Super-critical fluidoperations conditions (SCF) are advantageous because of the fastreaction kinetics, high conversion degrees, low viscosity, and stronglyreduced need for additional chemicals and catalysts. The disadvantage isthe need for high temperature and high pressure, and the correspondingcomplexity and cost associated with such operation conditions of thereactor. For a recent review of this technical area, the skilled readeris referred to Wen et al. in Progress in Natural Science 19 (2009),273-284.

Many SCF reactors are operating in continuous mode with a productionline i.e. not in a batch mode because of the need for large-scaleproduction of biofuel. A traditional way of scaling up a continuous flowproduction is by using a tubular reactor in which a pump is feeding oneend of a relatively long tube, typically consisting of a preheatingzone, a heated reactor zone and a cooling zone. The reaction time maythen be influenced, among other factors, by the flow rate and the tubelength. If long reaction time is needed either a very long tube, or avery low flow rate is needed. However, both of these solutions are inmost cases not feasible due to on one hand large costs and pressuredrops, and on the other hand low heat transfer efficiency, risk ofsedimentation/clogging and low productivity. Especially in the case ofbio-based slurries, it is well known that they have a Non-Newtonian(thixotropic) behaviour, and that their viscosity can increase severalorders of magnitude when the shear rate is approaching zero. Thus, atlow flow rates their viscosity will be very high and thus the pressuredrop, pumping resistance and inverse heat transfer will be very high.This will be a large challenge especially in the parts of the processwhere the temperature is relatively low, i.e. in transport and heatexchanger zones.

Hence, an improved method for operating a production system forproducing biofuel from biomass would be advantageous, and in particulara more efficient and/or reliable method would be advantageous.

OBJECT OF THE INVENTION

It is a further object of the present invention to provide analternative to the prior art.

In particular, it may be seen as an object of the present invention toprovide a method for operating a production system for producing biofueland bio-based chemicals from biomass that solves the above mentionedproblems of the prior art with reaction time, low production, clogging,and/or limited scalability of the production line.

SUMMARY OF THE INVENTION

Thus, the above described object and several other objects are intendedto be obtained in a first aspect of the invention by providing a methodfor producing bio-fuel (BF), or other bio-based chemicals, from biomass(BM), preferably a high-viscosity biomass, in a continuous flowproduction line, preferably using thermo-35 chemical conversion of thebiomass, the production line comprising:

-   -   pumping means (PM) capable of pumping the biomass through the        production line under a controlled pressure and flow,    -   heating means (HM) in thermal contact with a first part of the        production line for controlling the temperature in the        production line, and    -   cooling means (CM) in thermal contact with a second part of the        production line for cooling the biomass under conversion,        the method comprising:    -   operating the pumping means, the heating means and the cooling        means so that, at least part of, the production line is under        supercritical fluid conditions (SCF), optionally at        near-supercritical fluid conditions, so as to induce biomass        conversion in a conversion zone (CZ) within the production line,        and    -   operating the pumping means so that, at least part of, the        production line is in an oscillatory flow (OF) mode, wherein a        local oscillatory flow rate of the biomass under conversion is        superimposed on the average flow rate through the production        line.

The invention is particularly, but not exclusively, advantageous forproviding a method for producing biofuel from a high-viscosity biomass,e.g. from lingo-cellulosic biomass, high cellulose containing material,lignin containing biomass, manure, food production by-products, andwaste water sludge. This is essentially performed by an advantageouscombination of two kinds of different operating modes; supercriticalfluid (SCF) conditions and oscillatory flow (OF). The present inventionmay be capable of solving problems in this technical field with reactiontime, clogging of reactors, and/or scalability of production to largereactors. The oscillating flow enables that the flow in, at least partof, the production line increases resulting in a lower viscosity. Lowerviscosity enables higher heat transfer from the heating means to thebiomass, which, in turn, improves the effectiveness of the productionline. The lower viscosity of the biomass also makes it possible tooperate the production line at lower average flow rate, which maytherefore raise the overall reaction time in the production line, whileat the same time yielding a high conversion. The supercritical fluidconditions in combination with the oscillatory flow thus facilitatefaster and/or improved conversion of the biomass.

The method and production line according to the present invention isparticularly suited for yielding biofuel, e.g. biodiesel, for use inlater energy production. The invention is however also suited foryielding other products, broadly defined bio-based chemical product frombiomass, such as phenols, other aromatic compounds, substituted furanes,lactates, acrylates and oligomeric versions of the afore mentioned.

In context of the present invention, a supercritical fluid may bedefined as a substance at temperature and pressure above its criticalpoint where distinct and separate liquid and gas phase do not exist.Super-critical (near) fluids are fluids existing above the criticalpoint in the pressure-temperature range. Near critical fluids may befluids above 60%, preferably above 70%, or more preferably above 80% ofthe absolute temperature and/or pressure of the critical point. As theskilled reader will recognise, the dual properties of the liquid and thegas phases may then be exploited for enhanced biofuel production, orother bio-based chemical products. Preferably, the temperature in theconversion zone may be at least 500 K, preferably at least T 600 K, morepreferably at least 650 K. Additionally or alternatively, the pressurein the conversion zone may be at least 13 MPa, preferably at least 17MPa, more preferably at least 22 MPa. The critical temperature andpressure of water is approximately 647K and 220 bar, for ethanol it isapproximately 514K og 60 Bar, and for methanol it is approximately 513Kand 80 bar, respectively. For mixtures of fluids, a reasonable estimateof the critical temperature and pressure can often be found by aweighted average between the molecular amounts of the fluid components.For information on supercritical fluids, the skilled reader is referredto Brunner, G. (2010). “Applications of Supercritical Fluids”. AnnualReview of Chemical and Biomolecular Engineering 1: 321-342 andreferences cited therein.

Oscillatory flow may be defined by the resulting flow having an averageflow rate determined by the feed rate into the production line, and alocal flow rate superimposed on the average flow rate determined by theoscillating pressure of the pumping means, preferably the oscillatorypressure being provided by dedicated oscillatory flow inducing means.Notice that in several prior art applications of oscillatory flow, e.g.in oscillatory flow reactors (OFR), the tubes of the reactor comprisesequally spaced orifice plate baffles that separates the reactor intoeffectively separate ‘stirred tanks’ with possible positive impact onthe mixing and hence conversion yields. However, the present inventionis not intended, though not excluded, for having such internal bafflesas they may typically negatively influence ease of manufacturing andlater cleaning and maintenance. The oscillatory flow may becharacterized by the various features including, but not limited to,stroke length of the piston, or equivalent, generating the oscillatoryflow, frequency, resulting shear rate, the average flow rate (fromlittle to high flow flow) in combination with the local flow rate, etc.

Within the context of the present invention, it is to be expected thatthe oscillatory flow superimposed on the average flow through theproduction line may be damped from the imposing site or point downthrough the production line, i.e. in some embodiments only a part of theproduction line may be said to be in oscillatory flow (OF) mode if thedamping completely or almost completely dampens the oscillatory flowout. In particular, it is contemplated that the part of the productionline being under (near) supercritical fluid conditions (SCF) maysignificantly dampen the oscillatory flow due to the combined gas andliquid-like properties of the supercritical fluid facilitating suchdamping.

Within the context of the present invention, it is further to beunderstood that biomass may include materials and products of biologicalorigin, typically available in large quantities/bulk from living orrecently living organisms.

Within the context of the present invention, it is to be understood thata production line is an extended processing system where the enteringbio-mass is conveyed by suitable transportation means through a numberof process steps, where at each step one or more processes occur, e.g.pressurizing, heating, conversion of bio-mass, cooling, depressurizing,etc., and eventually the resulting biofuel, or other bio-basedchemicals, is conveyed out of the production line. The term productionline may be synonymous with a production system for carrying out themethod according to the invention.

By the term ‘continuous flow’, it is particularly to be understood thatthe bio-mass flows with a non-zero flow rate through the productionline, preferably all the time or most of the time during operation ofthe production line. Thus, continuous flow may be considered, at leastfor some purposes, as the opposite of a batch-like process.

Within the context of the present invention, the thermo-chemicalconversion includes, but is not limited to, hydrothermal conversion ofbiomass. Hydrothermal conversion of biomass may, without being bound toany specific theory, be defined as chemical processes performed atelevated temperatures in the presence of a liquid phase, such as wateror other polar solvents that will convert biomass into lower molecularweight components, such as biofuels and other chemical mixtures.

Within the context of the present invention, shear thinning fluids mayinclude, but not being limited to, thixotropic and pseudoplastic fluids,i.e. fluids that will exhibit shear thinning either depending on shearrate alone (pseudoplastic) or shear rate and time (thixotropic) Aspecial type of shear thinning also relevant for biomass slurries isBingham plastic behaviour in which the material behave solid-like up toa certain shear stress. It should be mentioned that biomass typicallyhas highly shear thinning properties, which may significantly influencethe viscosity and thereby pressure drop and heat conductivity throughthe biomass i.e. changing the shear rate may cause changes in viscosityby several orders of magnitude. For further details on the rheologyproperties of bio-mass, the skilled reader is for example referred toRheology measurements of a biomass slurry: an inter-laboratory study byJonathan J. Stickel et al. in Rheol Acta (2009) 48:1005-1015, which ishereby incorporated by reference in its entirety.

In an advantageous embodiment, wherein the production line may compriseoscillatory flow inducing means (OFIM) in fluid contact with theproduction line, the OFIM preferably being distinct from the pumpingmeans. Preferably, the oscillatory flow inducing means may comprise:

-   -   one or more positive displacement pumps, such as        membrane/diaphragm based pumps, or piston based pumps,    -   one or more velocity pumps, such as centrifugal type pumps,    -   one or more impulse pumps,    -   one or more gravity pumps,    -   one or more steam pump, and/or    -   one or more valveless pumps        for inducing oscillatory flow in the production line.

Optionally, when operating the production line in an oscillatory flow(OF) mode it may comprise that the local flow has an alternatingdirection of flow with an oscillatory frequency (f_osc) through at leastpart of the production line, preferably in at least said first part 1 ofthe production line, and/or in at least part of the conversion zone(CZ). In some embodiments, the entire production line may be operated ina OF mode.

In one embodiment, the oscillatory flow inducing means (OFIM) may bepositioned in fluid contact with the production line at, or near, thesaid first part of the production line and operated for inducing anoscillatory flow in at least part of the production line, preferably inat least said first part of the production line for increasing the heattransfer, and/or in at least part of the conversion zone (CZ) forincreasing the conversion efficiency.

In another alternative or combined embodiment, the oscillatory flowinducing means (OFIM) may be positioned in fluid contact with theproduction line at, or near, the said second part of the production lineand operated for inducing an oscillatory flow, preferably in at leastsaid first part and/or said second part of production line and/or in atleast in part of the conversion zone (CZ) for increasing the conversionefficiency.

In some embodiments, the temperature, the pressure, and the flow ratemay be controlled so as to subject the biomass to a sufficient shearstress for obtaining shear thinning properties, or near shear thinningproperties, of the biomass at least in part of production line,preferably in at least said first part of production line and/or in atleast in part of the conversion zone (CZ), In some embodiments, theentire production line may be operated so that the biomass has shearthinning properties, or near shear thinning properties.

Preferably, the conversion zone of the production line undersupercritical fluid conditions (SCF) may be positioned in the productionline between the said first part and the said second part of theproduction line to improve heating and cooling effectiveness.

Optionally, the production line, at least in the conversion zone (CZ),may have a tubular (internal) structure, preferably with a substantiallyunchanged inner diameter in the conversion zone (CZ), in order to lowerclogging, ease maintenance and cleaning, and/or for simplifying themanufacturing process.

In some embodiment, the heating means may be supplied with heat fromsaid cooling means via heat exchanging means for increased efficiency.Particularly, the production line in said first part and/or second parthave a tubular structure, the heating exchanging means may comprise aentity made of a heat conduction material, preferably manufactured in ametal or a metal alloy, surrounding the tubular structures in both thefirst and/or the second part for conducting the heat from the secondpart to the first part in the production line. Furthermore, the heatingexchanging means may comprise a fluid cooling medium for conducting theheat from the second part to the first part in the production line viafluid flow in the heat exchanging means, the fluid flow in the heatexchanging means preferably being arranged in a counter-flow relative tothe biomass under conversion in the production line for furtherincreased efficiency.

Typically, the production line may comprise a depressurizing unit at anoutlet for the resulting biofuel (BF), or bio-based chemical, from theproduction line, by which the product is released in a semi-continuous,or continuous, manner from the production line and depressurized fromthe supercritical pressure in the production line. Advantageously, theoscillatory flow inducing means (OFIM) may then be operably connected tothe depressurizing unit, the pressure energy released duringdepressurizing being, at least partly, conveyed to the pumping means(PM) and/or the oscillatory flow inducing means (OFIM) for increasedpump efficiency.

In one embodiment, one, or more, hydraulic accumulators may be arrangedas a pressure storage reservoir for absorbing pressure energy from thedepressurizing unit for temporally storing pressure energy, and the one,or more, hydraulic accumulators being arranged for conveying, at leastpartly, the stored pressure energy to the oscillatory flow inductionmeans (OFIM) thereby reusing the stored pressure energy resulting inimproved cost efficiency of the production line.

Advantageously, the biomass feed into the production line may beselected from the group consisting of: lignin-based material,lignocellulosic biomass, high cellulose containing material, lignincontaining biomass, manure, food production by-products, and waste watersludge. Some biomass type may have an initial viscosity being at least0.01, preferably at least 0.1, more preferably at least 1 PaS. Theskilled person in rheology will appreciate that viscosity is not easy tomeasure because it can depend on a number of factors involved in themeasurement itself, in particular because biomass typically behaves likea non-Newtonian fluid. Accordingly, the initial viscosities listed abovemay depend on the measurement method as it will be understood andtherefore apply for several measurement methods useful for biomassviscosity.

In a second aspect, the invention further relates to a production linefor producing biofuel, or other bio-based chemicals, from biomass in acontinuous flow, preferably using thermo-chemical conversion of thebiomass, the production line comprising

-   -   pumping means (PM) capable of pumping the biomass through the        production line under a controlled pressure and flow,    -   heating means (HM) in thermal contact with a first part of the        production line for controlling the temperature in the        production line, and    -   cooling means (CM) in thermal contact with a second part of the        production line for cooling the biomass under conversion,        wherein the pumping means, the heating means and the cooling        means are arranged for being operated so that, at least part of,        the production line is under supercritical fluid conditions        (SCF), optionally at near-supercritical fluid conditions, so as        to induce biomass conversion in a conversion zone (CZ) within        the production line, and        wherein the pumping means are arranged for being operating so        that, at least part of, the production line is in an oscillatory        flow (OF) mode, wherein a local oscillatory flow rate of the        biomass under conversion is superimposed on the average flow        rate through the production line.

In a third aspect, the invention relates to a computer program productbeing adapted to enable a computer system comprising at least onecomputer having data storage means in connection therewith to control aproduction line according to the first and/or second aspect of theinvention.

This aspect of the invention is particularly, but not exclusively,advantageous in that the present invention may be accomplished by acomputer program product enabling a computer system to carry out theoperations of the production line of the first and/or second aspect ofthe invention when down- or uploaded into the computer system. Such acomputer program product may be provided on any kind of computerreadable medium, or through a network.

In a preferred embodiment, the computer program product may be furtherarranged for receiving inputs related to at least temperature, pressureand flow rate through the production line, and based on said inputfurther being arranged for outputting an apparent value of viscosity forthe biomass entering the production line, the computer program productfurther enabling adjustment (either manually, semi-automatic orautomatic) of the production line based on said apparent value ofviscosity for the biomass. This is particular advantageous because itfacilitates real-time measurement of viscosity of the incoming biomasswhich is quite important for operating the production line at optimum ornear optimum performance.

The first, second and third aspect of the present invention may each becombined with any of the other aspects. These and other aspects of theinvention will be apparent from and elucidated with reference to theembodiments described hereinafter.

BRIEF DESCRIPTION OF THE FIGURES

The invention will now be described in more detail with regard to theaccompanying figures. The figures show one way of implementing thepresent invention and are not to be construed as being limiting to otherpossible embodiments falling within the scope of the attached claim set.

FIG. 1 is a schematic drawing of the production line according to thepresent invention,

FIG. 2 is a schematic graph of the time versus the position forillustrating oscillatory flow,

FIG. 3 is another schematic drawing of the production line withoscillatory flow inducing means according to the present invention,

FIGS. 4A, 4B and 4C show other schematic drawings of the production linewith oscillatory flow inducing means of the piston type according to thepresent invention,

FIG. 5 shows yet another schematic drawings of part of the productionline with oscillatory flow inducing means comprising a reverse gear pumpaccording to the present invention,

FIG. 6 shows yet another schematic drawing of part of the productionline with oscillatory flow inducing means comprising a hydraulicaccumulator according to the present invention,

FIG. 7 shows a depressurizing unit according to the present invention,

FIG. 8 is a more detailed schematic drawing of a production lineaccording to the present invention,

FIG. 9 shows a segment of a heat exchanger according to the presentinvention, and

FIG. 10 is a flow-chart of a method according to the invention.

DETAILED DESCRIPTION OF AN EMBODIMENT

FIG. 1 is a schematic drawing of the production line 10 according to thepresent invention. The invention also relates to a method for producingbio-fuel BF 5 (as indicated by arrow in the lower part of the productionline) or other bio-based chemicals, from biomass BM 4 entering theproduction line (as also indicated with arrow in the upper part of theFigure). The biomass is preferably a high-viscosity biomass, e.g. with aviscosity of 0.1 PaS or higher. The production line 10 is advantageouslyoperated in a continuous flow. The production line 10 preferably usesthermo-chemical conversion of the biomass. The conversion may optionallybe assisted by added chemicals, e.g. catalysts, acids or bases, etc.Appropriate solvents may also be added, e.g. water or other polarsolvents. The production line comprises pumping means 20 PM, e.g. one ormore pumps, capable of pumping the biomass 4 through the production lineunder a controlled pressure, P, and flow. The production line 10 alsocomprises heating means HM in thermal contact with a first part 1 of theproduction line for controlling the temperature, T, in the productionline. Additionally, the production line comprises cooling means CM 40 inthermal contact with a second part 2 of the production line 10 forcooling the biomass under conversion.

The method according to the invention particularly comprises operatingthe pumping means 20, the heating means 30 and the cooling means 40 sothat, at least part of, the production line 10 is under supercriticalfluid conditions (SCF), optionally at near-supercritical fluidconditions, so as to induce biomass conversion in a conversion zone CZwithin the production line. In FIG. 1, the conversion zone isschematically shown as being smaller than the part of the productionline being operated at SCF (or near SCF) conditions, but in otherembodiments the conversion zone and the part of the production lineunder SCF conditions may be the same (i.e. overlapping and coinciding),or substantially the same.

The method according to the invention further comprises operating thepumping means PM 20 so that, at least part of, the production line 10 isin an oscillatory flow OF mode, wherein a local oscillatory flow rate ofthe biomass under conversion is superimposed on the average flow ratethrough the production line 10.

Thus, in some embodiments the whole production line 10 is operated in anoscillatory flow OF mode, including the supercritical fluid SCF zone andthe conversion zone CZ. In other embodiments, only parts of theproduction line 10 is operated in an oscillatory flow OF mode, forexample the part of the production line 10 from the pumping means PM 20inducing the oscillatory flow and parts of the conversion zone CZ. Insome embodiments, the oscillatory flow mode may extend into parts of thesupercritical fluid SCF zone but not covering the conversion zone CZ dueto the damping taking place of the oscillatory flow in the supercriticalfluid SCF zone.

In FIG. 1, the flow direction through the production line 10 isschematically indicated by arrows A1 and A2, though it should beremembered that the imposed oscillatory flow OF may cause theinstantaneous flow to be shortly in the opposite direction in theproduction line 10, though the average flow direction will be asindicated.

The production line 10 shown is schematically indicated in FIG. 1, butthe skilled person is referred to e.g. FIG. 8 for a more detailedembodiment of a production line 10. It may be mentioned that varioussteps, including but not limited to, such as pre-treatment, preheating,separation, purification, chemical upgrading incl. hydrogenation, arealso foreseen within the context of the present invention for producingbiofuel, or other bio-based chemicals, from biomass as it will beappreciated by the skilled person once the general teaching andprinciple of the present invention has been acknowledged.

Within the context of the present invention, the pumping means PM 20 maycomprise electrically driven, hydraulically driven, and/or pneumaticallydriven pumps. The pumps may be positive displacement pumps, e.g. pistonbased pumps, or velocity pumps, e.g. centrifugal type pumps. The pumpingmeans may include extruders for feeding biomass under pressure, oreccentric screw pumps. Alternative pumping means include impulse pumps,gravity pumps, steam pumps, and valveless pumps.

FIG. 2 is a schematic graph of the time (vertical axis) versus theposition (horizontal axis, ‘reactor’ being synonymous with theconversion zone, CZ) for illustrating some aspects of the oscillatoryflow OF according to the present invention. As seen in the graph, theaverage flow rate is constant but the local flow rate is oscillating.The position, in the example shown in FIG. 2, is going back and forthi.e. local flow rate is alternating direction between forward andbackwards (position being larger and smaller, respectively) therebyincreasing the reaction time in the production line 10. The average flowdirection is, however, positive i.e. the flow through the productionline will take place as indicated by arrows A1 and A2 in FIG. 1.

According to the invention further the pumping means PM 20 are operatedso that, at least part of, the production line 10 is in an oscillatoryflow OF mode, the local oscillatory flow rate of the biomass underconversion is superimposed on the average flow rate through theproduction line as shown in the graph of FIG. 2. In advantageousembodiments, the local flow rate and average flow rate may, at least tosome extent, be adjusted independently of each other enabling evenbetter yield of the product i.e. biofuel. When operating the productionline 10 in an oscillatory flow OF mode, the local flow may thus have analternating direction of flow through the production line 10 at least inpart of the conversion zone CZ. The alternating direction may changewith an oscillatory frequency, f_osc, set by the operator of theproduction line and/or set automatically by control means (not shown) ofthe production line. In some embodiments, the oscillatory flow may havejust a forward direction.

FIG. 3 is another schematic drawing of the production line withoscillatory flow inducing means OFIM 50 and 50′ according to the presentinvention but otherwise similar to FIG. 1. Thus, the production line 10comprises an oscillatory flow inducing means, e.g. two membrane-basedpumps with membranes 51 schematically indicated. The pumps 50 and 50′are in fluid contact with the production line, and the oscillatory flowinducing means are different from said pumping means 20, the pumpingmeans 20 providing the average flow through the production line 10. Theoscillatory flow inducing means 50 and 50′ may thus comprise one, ormore, membrane(s) 51 as shown for inducing the oscillatory flow throughthe production line. In the embodiment shown, the membrane-based pumps50 and 50′ are provided both at the biomass 4 inlet and near thebio-fuel 5 outlet, respectively, as schematically shown. In this way,the oscillatory flow can better be maintained through the productionline by such an up-stream and downstream oscillatory flow provider.

The oscillatory flow inducing means 50 is positioned in fluid contactwith the production line 10 at, or near, the first part 1 of theproduction line and operated for inducing an oscillatory flow to atleast in part of the conversion zone CZ. Similarly, the oscillatory flowinducing means 50′ is positioned in fluid contact with the productionline at, or near, the second part 2 of the production line 10 andoperated for inducing an oscillatory flow back stream through theproduction line 10 back to at least part of the conversion zone CZ. Inembodiments of the invention, only one of the OFIM pumps may be used,i.e. either pump 50 or pump 50′.

As seen in FIGS. 1 and 3, the conversion zone CZ of the production lineunder (near) supercritical fluid conditions SCF is positioned at part 3of the production line between the first part 1 and the second 2 part ofthe production line where the heating and cooling, respectively, takeplace.

Within the context of the present invention, the oscillatory flowinducing means may comprise electrically driven, hydraulically driven,and/or pneumatically driven pumps. The pumps may be positivedisplacement pumps, e.g. piston based pumps or membrane based pumps, orvelocity pumps, e.g. centrifugal type pumps. The oscillatory flowinducing means of FIG. 3 are membrane-based pumps, below various othertypes of pumps are illustrated, though the skilled person will readilyunderstand that several other types of pumps may be applied within thecontext of the present invention once the general teaching and principleof the invention has been understood.

FIGS. 4A and 4B show other schematic drawings of the production linewith oscillatory flow inducing means OFIM of the piston type accordingto the present invention. These means for providing oscillatory flow mayin some embodiments also be applied for providing the average flowthrough the production line 10.

FIG. 4A schematically shows a production line 10 with a singlepiston-based pump OFIM 51 i.e. a positive displacement pump beingpositioned upstream relative to the inlet of biomass 4 BM.

FIG. 4B schematically shows a production line 10 with two piston-basedpumps OFIM 52 and 53 being positioned upstream and downstream,respectively, relative to the inlet of biomass 4 BM. This is technicallysimilar to the double membrane based embodiment of FIG. 3.

FIG. 4C schematically shows another production line 10 with two doublepiston-based pumps OFIM 52′ and 53′ being positioned upstream anddownstream, respectively, relative to the inlet of biomass 4 BM. Asfurther development of the embodiment of FIG. 4B, the pumps OFIM 52′ and53′ each have a double piston based functionality with the respectiveset of pistons generally working in counter-phase to neighbouring pistonto create the most optimum oscillatory flow through the production line10. In such a setup the double pumps will be able to act as a combinedfeeding and oscillation pump and a combined depressurization andoscillation pump, respectively. The associated actuators are shown nextto each piston with a double-arrow as will be understood by the skilledperson in hydraulics. Thus, the first set of pistons 52′a and 52′b maywork in counter-phase to each other, their corresponding workingpressure being controlled by the associated valves as schematicallyindicated in FIG. 4C, and similarly for the other set of pistons 53′aand 53′a′.

FIG. 5 shows yet another schematic drawing of part of the productionline 10 with oscillatory flow inducing means OFIM 55 comprising areverse gear pump according to the present invention. Technically, asingle entity can thereby produce both oscillatory flow both upstreamand downstream relative to the average flow direction, the average flowdirection being schematically indicated by arrow A1. The dotted lineafter the arrow A1 indicates that only part of the production line 10 isshown here. When implementing this embodiment, the skilled person shouldconsider the issue of backflow i.e. whether, and to what degree, theproduced bio-fuel on the downstream side of the pump 55 is allowed toflow back into the starting part of the production line. If sufficientpiping distances are implemented into the production line this may besolved.

FIG. 6 shows yet another schematic drawing of part of the productionline 10 with oscillatory flow inducing means OFIM 56 and 57 comprising ahydraulic accumulator 70 according to the present invention. OFIM 56 and57 may be implemented as so-called media separators known in hydraulics,commercial vendors of such equipment being for example HYDAC, Parker,HiP (High Pressure Equipment Company), etc. This embodiment has theadvantage that the driving force for the oscillatory movement only hasto overcome the pressure difference between the hydraulic accumulatorand the process line. The pressure difference may be in the range of 5to 100 bar depending on the needed driving force to overcome thefriction in the flow pattern of the system. The described use ofhydraulic accumulators strongly reduces the energy consumption and pumpinvestments costs. Possible accumulators include, but is not limited to,separator-less accumulators, gas charged accumulators (piston orbladder), spring-loaded piston accumulators, weight loaded accumulators,and diaphragm accumulators.

The production line comprises a depressurizing unit and take off unit(not shown in FIG. 6 but see FIG. 7) at an outlet for the product fromthe production line, by which the product is released in asemi-continuous, or continuous, manner from the production line anddepressurized from the high pressure in the production line 10. Thedepressurising unit may comprise the piston OFIM 57 on the downstreamside by absorbing at least part of the pressure via the piston. Thepressure energy may subsequently be temporally stored in accumulator 70.Thus, the depressurizing unit is operably connected to a hydraulicaccumulator arranged as a pressure storage reservoir for absorbingpressure energy and temporally storing the pressure energy, thehydraulic accumulator 70 being further arranged for releasing the storedpressure energy to the oscillatory flow inducing means OFIM 56 viahydraulic circuit means, in particular the switch valve 71, e.g. 4/2switch valve, so as to reuse the hydraulic energy from the productionline. Appropriate vents for operating the hydraulic accumulator 70 arealso shown in FIG. 6.

FIG. 7 shows a depressurizing unit 170 according to the presentinvention. The bio-fuel BF 5 is initial under a high pressure, asindicated by symbol HP, after being conveyed away from the supercriticalfluid SCF pressurized zone. The pistons 72 and 72′ absorb at least partof the high pressure in the fluid reservoir tank 73 with an open topconnected to the pistons 72 and 72′ by appropriate fluid connectingmeans, in particular a distributor valve 74, e.g. a 4/2 four way valve,and a constant flow valve 75. The tank 73 could alternatively be closedwith a valve to the surroundings. The combined action of the tank 73 andthe pistons 72 and 72′ is to function as a damper as it will beappreciated. The product BF 5 is conveyed from the depressurization unit170 to the product tank that also can act as a gas separation unit,allowing the gaseous byproducts to be analyzed.

The depressurizing unit may alternatively, or additionally, comprise oneor more of the following depressurizing means; needle valves, capillarytubes etc. In particular, various pumps and combination thereof may beused, such as an electrically driven, hydraulically driven, and/orpneumatically driven pump. The pumps may be positive displacement pumps,e.g. piston based pumps, membrane (diaphragm) based pumps, gear pumps,progressing cavity pump, impeller based pumps, rotary lobe pumps, rotaryvane pumps, or velocity pumps, e.g. centrifugal type pumps. Especially,they may have double action.

FIG. 8 is a more detailed schematic drawing of a production line 10according to the present invention. FIG. 8 is a so-called Piping,Instrumentation and Design (PID) diagram, well-known in hydraulics, ofthe production line 10. Various pressure gauges, valves, safety valves,gas separator, product tanks, CIP system, and sensors etc. are shown inFIG. 8 but will not be separately explained apart from certain elementsof the invention.

Pumping means 120 are capable of pumping the biomass 4 BM through theproduction line under a controlled pressure and flow. Initially, thebiomass BM enters a heat exchanger 150 (from the left in FIG. 8). On theprimary side (not shown) of the heat exchanger the biomass will then beheated from hot biofuel 5 BF from the secondary side (shown), thebiofuel entering from the top of the heat exchanger as seen in FIG. 8.Thus, some heating will take place.

Secondly, heating means HM 130 in thermal contact with the productionline 10 facilitate control of the temperature and thereby resulting infurther heating of the biomass. The heated biomass then enters thereactor part 104 REAC of the production line 10 under (near)supercritical fluid condition. In the reactor, the biomass will beconverted to biofuel 5 BF. The drawing in FIG. 8 is schematic so theextent of the conversion zone CZ may not be accurate but merelyillustrative.

Thus, the production line is operated so that the pumping means 120 and150, the heating means and the cooling means so that, at least part of,the production line is under supercritical fluid conditions SCF,optionally at near-supercritical fluid conditions, so as to inducebiomass conversion in a conversion zone CZ, here reactor 104 REAC,within the production line 10.

Additionally, the production line 10 is operated so that the pumpingmeans 120 and the oscillatory flow inducing means 150 are able to keep,at least at part of, the production line in an oscillatory flow OF mode,wherein a local oscillatory flow rate of the biomass under conversion issuperimposed on the average flow rate through the production line 10.

As shown in FIG. 8, there may further be provided cooling means CM 140in thermal contact with a second part of the production line for furthercooling the biofuel BF 5 after leaving the heat exchanger 150.Optionally, the heat extracted from the biofuel 5 BF in cooling means140 may be re-used in heating means 130.

Suitable heating exchangers 150 and the combined heat exchanger ofcooler 140 and heater 130 may include, but is not limited to,tube-by-tube configuration joined in a highly thermally conductivematerial, a segmented heat exchanger, heat exchanger using a coolingmedium, such as oil, salt melting medium, hot water medium, etc., as theskilled person in thermodynamics would readily contemplate for use whendesigning, implementing and operating a production line for producingbiofuel, or other bio-based chemicals, from biomass according to thepresent invention.

It should be noted that even though the production line 10 shown in FIG.8 is operated at least partly in an oscillatory flow OF, cf. FIG. 2 andcorresponding description thereof above, by carefully controlling thepumping means 120 and the OFIM 150, there is no need for designing thetubes in the production line 10 with baffles to achieve oscillatoryflow. On the contrary, it is intended that the pipes or tubes may haveessentially the same diameter, at least on parts or sections of the line10, providing easier design, manufacturing, operating (e.g. no clogging)and/or maintenance, especially cleaning.

It may be mentioned that the depressurizing unit 170 may be functionallyconnected to the OFIM 150 and the pumping means 120 for optionallyre-using the energy in the high pressure product of biofuel BF 5.Particularly, the depressurizing unit 170 can be fluid-wise connected tothe OFIM 150 with an additional pressure accumulator for temporallystoring the pressure energy, and later reuse the pressure energy forcreating oscillatory flow in the production line, as explained in moredetail in connection with FIG. 6 above.

In a production system for producing bio-fuel etc. according to thepresent invention as depicted in FIG. 8, the system comprisingapproximately 124 m of UNS6625 tubing with an inside diameter of 14 mmand where the feed was passed through 24 m of heat exchanger (cold side)tube, 16 m of trimheater tube, 60 m of reactor tube and finally 24 m ofheat exchanger (hot side) tube, a number of preliminary experiments wereconducted:

The heat transfer was performed through a large number of custom-madeheat clamps made out of cast iron, cf. FIG. 9 for an example, to fit thethermal expansion of the tube alloy with a wall to wall distance betweenthe tubes of 26 mm. The preliminary experiments conducted with a reactortemperature of 575 K and pure water as the reference fluid showed thatthe oscillation reduced the heat loss by 20% in the heat exchanger ascompared to the same flow with no oscillation (82% recovery vs 78% forno oscillation).

Furthermore, experiments with fibrous biomass (10% milled MiscantusGigantus in water containing 1.5% potassium hydroxide) at the abovetemperature range showed that there was a 10-20% reduction in feedpressure needed to obtain a steady flow of 25l/hr, indicating asignificant reduction in dynamic viscosity of the feed as expected whenimplementing the present invention.

FIG. 9 shows a segment of a heat exchanger 250 according to the presentinvention in three planar view and a perspective view. The segment 250may be manufactured by joining two tube parts 251 a and 251 b togetherin solid matrix 252 of relatively good heat conducting material, such asa steel alloy or similar material. A plurality of such segments 250 mayform a heat exchanger 150 as shown in FIG. 8. Similarly, the combinedheat exchanger of cooling means 140 and heating means 130 may beimplemented by such a plurality of segments 250. This has the advantagethat at least part of the invention may be manufactured by relativelysimple elements keeping cost at a low level. In particularly, it may benoted that the dimensions of the heat segment 250 should be sufficientlystrong enough to sustain the production line operating at (near)supercritical pressures and temperatures of the biomass 4 BM. Thedimensions shown in FIG. 9 are in millimetres (mm).

FIG. 10 is a flow-chart of a method according to the invention forproducing bio-fuel 5 BF, or other bio-based chemicals, from biomass 4BM, preferably a high-viscosity biomass, e.g. least 0.1 PaS, in acontinuous flow production line 10, preferably using thermo-chemicalconversion of the biomass, the production line comprising:

-   -   pumping means PM 20 or 120 capable of pumping the biomass        through the production line under a controlled pressure and        flow,    -   heating means HM 30 or 130 in thermal contact with a first part        1 of the production line for controlling the temperature in the        production line, and    -   cooling means CM 40 or 140 in thermal contact with a second part        2 of the production line for cooling the biomass under        conversion,        the method comprising:

S1 operating the pumping means, the heating means and the cooling meansso that, at least part of, the production line is under supercriticalfluid conditions SCF, optionally at near-supercritical fluid conditions,so as to induce biomass conversion in a conversion zone CZ, e.g. reactor104 REAC in FIG. 8, within the production line, and

S2 operating the pumping means so that, at least part of, the productionline is in an oscillatory flow OF mode, wherein a local oscillatory flowrate of the biomass under conversion is superimposed on the average flowrate through the production line.

In short, the present invention discloses a method for producingbio-fuel BF from a high-viscosity biomass using thermo-chemicalconversion of the biomass in a production line 10 with pumping means PM,heating means HM and cooling means CM. The method has the steps of 1)operating the pumping means, the heating means and the cooling means sothat the production line is under supercritical fluid conditions SCF toinduce biomass conversion in a conversion zone CZ within the productionline, and 2) operating the pumping means so that, at least part of, theproduction line is in an oscillatory flow OF mode. The invention isadvantageous for providing an improved method for producing biofuel froma high-viscosity biomass. This is performed by an advantageouscombination of two operating modes: supercritical fluid SCF conditionsand oscillatory flow OF.

The invention can be implemented by means of hardware, software,firmware or any combination of these. The invention or some of thefeatures thereof can also be implemented as software running on one ormore data processors and/or digital signal processors.

The individual elements of an embodiment of the invention may bephysically, functionally and logically implemented in any suitable waysuch as in a single unit, in a plurality of units or as part of separatefunctional units. The invention may be implemented in a single unit, orbe both physically and functionally distributed between different unitsand processors.

Although the present invention has been described in connection with thespecified embodiments, it should not be construed as being in any waylimited to the presented examples. The scope of the present invention isset out by the accompanying claim set. In the context of the claims, theterms “comprising” or “comprises” do not exclude other possible elementsor steps. Also, the mentioning of references such as “a” or “an” etc.should not be construed as excluding a plurality. The use of referencesigns in the claims with respect to elements indicated in the figuresshall also not be construed as limiting the scope of the invention.Furthermore, individual features mentioned in different claims, maypossibly be advantageously combined, and the mentioning of thesefeatures in different claims does not exclude that a combination offeatures is not possible and advantageous.

1. A method for producing bio-fuel, or other bio-based chemicals, frombiomass under continuous flow comprising: operating a production linehaving a tubular reactor, pumping means (PM) capable of pumping thebiomass through the tubular reactor under a controlled pressure andflow, heating means (HM) in thermal contact with a first part of thetubular reactor for controlling the temperature in the tubular reactor,and cooling means (CM) in thermal contact with a second part of thetubular reactor for cooling the biomass under conversion, in a mannersuch that the flow in at least part of the tubular reactor oscillatessuch that local flow has alternating direction between forward andbackward, resulting in lower viscosity of the biomass and higher heattransfer; and thermo-chemically converting the biomass in the tubularreactor.